​Zika is starting to spread on the US mainland — here's how bad it could get

A Miami-Dade County mosquito control worker sprays around a home in the Wynwood area of Miami on August 1, 2016. The CDC is concerned mosquito control methods aren't working as well as they should.Alan Diaz/AP
Zika virus has finally made its way to the US mainland, and the virus is now spreading locally in Miami. That means people are getting the virus from American mosquitoes, not just ones that have bitten them while they're abroad.

The Centers for Disease Control and Prevention (CDC) has even warned pregnant women not to travel to the Miami neighborhood where local cases have been detected.

That may sound scary, but it's not a surprise. Experts expected that the virus would start circulating in Florida.

The question now is: How far will Zika spread across the US?

The most likely answer is that it will spread through southern Gulf states where the mosquitoes that spread the virus are most active.

But the extent of the spread cannot be predicted precisely. It depends on how well public health officials can contain this first outbreak to Miami, and keep imported travel cases from turning into more outbreaks, David Pigott, a global health expert at the University of Washington, told Tech Insider.

"Never say never, but [a local outbreak is] a lot less likely to happen in New York or Washington, D.C. given our current knowledge than it is in Houston, or some cities across Louisiana, or other places in Florida," he said. "In terms of comparative risk, it's the southern states that are going to be the places where you're most likely to see it."

The virus is spread by the Aedes aegypti mosquito, which thrives in tropical areas and bites during the day. The Aedes albopictus mosquito can likely spread the disease, too, but that hasn't been observed in the Americas yet.

As you can see, the experts expect Zika to stick to Florida, parts of Georgia, Alabama, Mississippi, Louisiana, and Texas. Any other transmission across the US would likely be sporadic.

Another group of researchers modeled Zika's predicted spread, again based on environmental factors, but focused on international travel from infected areas. They predict the virus could circulate year-round in Florida and parts of Texas, and has the potential to pop up seasonally across a larger chunk of the US:

Finally, a third group of researchers predicted A. aegypti's potential spread of Zika in the US, also based on the environment and travel. The top half of the circle shows how abundant A. aegypti mosquitoes are in January, and the bottom half shows their potential abundance in July:

Anyone who is or is planning on becoming pregnant should wear bug spray on exposed skin where A. aegyptis mosquitoes are active, the CDC recommends.

Zika can be sexually transmitted, too, so couples should use condoms if they have traveled to or live in infected areas, as well.

But the biggest concern many experts have, Pigott told Tech Insider, is how little we know about Zika and its potential to take hold permanently in the Americas.

"Every time an imported case comes, you're rolling that dice in terms of a local outbreak occurring," Pigott said. "I think it could well be that these four [confirmed Florida] cases represent the tip of the iceberg, but I don't know if anyone knows how big that iceberg could potentially get."